The objectives of this trial conducted in early Parkinson's disease (PD) patients are:

To assess if patients with early Parkinson's disease (PD) can be successfully switched (overnight switching) from Pramipexole (PPX) Immediate Release (IR) to Pramipexole Extended Release (ER). A successful switch at a specific visit is defined as no worsening of the Unified Parkinsons Disease Rating Scale (UPDRS) parts II+III score by more than 15% from baseline and no drug-related adverse events leading to withdrawal;

To establish if this successful switch can be obtained with or without dose-adaptation;

To provide information about the conversion ratio (mg:mg) from Pramipexole IR to Pramipexole ER.

A Double-blind, Double-dummy, Randomized, Parallel Groups Study to Assess the Efficacy, Safety and Tolerability of Switching Patients With Early Parkinson's Disease (PD) From Pramipexole IR to Pramipexole ER or Pramipexole IR

Percentage of Patients Who Successfully Switched From Pramipexole Immediate Release (IR) to Pramipexole ER After a Possible Dose Adaptation, Full Analysis Set (FAS), Last Observation Carried Forward (LOCF) [ Time Frame: from baseline to week 9 ] [ Designated as safety issue: No ]

A successful switch was defined by no change of the Unified Parkinson's Disease Rating Scale (UPDRS) II+III by more than 15% from baseline to week 9, UPDRS II+III score ranging from 0 (no impairment) to 160 (worst impairment)

Secondary Outcome Measures:

Percentage of Patients Who Successfully Switched From Pramipexole IR to Pramipexole ER With no Dose Adaptation, FAS (LOCF) [ Time Frame: from baseline to week 4 ] [ Designated as safety issue: No ]

A successful switch was defined by no change of the UPDRS II+III by more than 15% from baseline to week 4, UPDRS II+III score ranging from 0 (no impairment) to 160 (worst impairment).

Change From Baseline in UPDRS Part II+III Total Score at Week 9, FAS (LOCF) [ Time Frame: Baseline and week 9 ] [ Designated as safety issue: No ]

Clinical Global Impression - Improvement on FAS, CGI-I was rated from 1: very much improved, to 7: very much worse, CGI-I responder are defined as being rated as 'unchanged', 'minimally improved', 'much improved', or 'very much improved', CGI-I non-responder are defined as being rated 'minimally worse', 'much worse' or 'very much worse'

Patient Global Impression - Improvement on FAS, PGI-I was rated from 1: very much better, to 7: very much worse, PGI-I responder are defined as being rated as 'unchanged', 'minimally better', 'much better', or 'very much better', PGI-I non-responder are defined as being rated as 'minimally worse', 'much worse', or 'very much worse'

Pramipexole dose should be optimized (according investigator¿s judgement), greater or equal to 1.5 mg/day, stable and equally divided 3 times per day, for a least 4 weeks prior to baseline visit (V2).

Patients willing and able to comply with scheduled visits, treatment plan, laboratory tests and other study procedures.

Signed informed consent obtained before any study procedures are carried out in accordance with International Conference on Harmonization - Good Clinical Practice (ICH-GCP) guidelines and local legislation).

Any of the following drugs within 4 weeks prior to the baseline visit: methylphenidate, cinnarizine, amphetamines.

Flunarizine within 3 months prior to baseline visit.

Known hypersensitivity to Pramipexole or its excipients.

Drug abuse (including alcohol), according to Investigator¿s judgement, within 2 years prior to screening.

Participation in other investigational drug studies or use of other investigational drugs within 4 weeks or five times the half-life of the investigational drug (whichever is longer) prior to baseline visit.

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Please refer to this study by its ClinicalTrials.gov identifier: NCT00558025